Lithium Secondary Batteries Containing Protected Particles of Anode Active Materials and Method of Manufacturing

ABSTRACT

Provided is anode active material layer for a lithium battery, comprising multiple particulates of an anode active material, wherein a particulate is composed of one or a plurality of particles of a high-capacity anode active material being embraced or encapsulated by a thin layer of a high-elasticity polymer having a recoverable tensile strain no less than 10% when measured without an additive or reinforcement, a lithium ion conductivity no less than 10-5 S/cm at room temperature, and a thickness from 0.5 nm (or a molecular monolayer) to 10 μm (preferably less than 100 nm), and wherein the high-capacity anode active material has a specific lithium storage capacity greater than 372 mAh/g (e.g. Si, Ge, Sn, SnO2, Co3O4, etc.).

FIELD OF THE INVENTION

The present invention relates generally to the field of rechargeablelithium battery and, more particularly, to the anode active materials inthe form of high-elasticity polymer-encapsulated particles and theprocess for producing same.

BACKGROUND OF THE INVENTION

A unit cell or building block of a lithium-ion battery is typicallycomposed of an anode current collector, an anode or negative electrodelayer (containing an anode active material responsible for storinglithium therein, a conductive additive, and a resin binder), anelectrolyte and porous separator, a cathode or positive electrode layer(containing a cathode active material responsible for storing lithiumtherein, a conductive additive, and a resin binder), and a separatecathode current collector. The electrolyte is in ionic contact with boththe anode active material and the cathode active material. A porousseparator is not required if the electrolyte is a solid-stateelectrolyte.

The binder in the binder layer is used to bond the anode active material(e.g. graphite or Si particles) and a conductive filler (e.g. carbonblack or carbon nanotube) together to form an anode layer of structuralintegrity, and to bond the anode layer to a separate anode currentcollector, which acts to collect electrons from the anode activematerial when the battery is discharged. In other words, in the negativeelectrode (anode) side of the battery, there are typically fourdifferent materials involved: an anode active material, a conductiveadditive, a resin binder (e.g. polyvinylidine fluoride, PVDF, orstyrene-butadiene rubber, SBR), and an anode current collector(typically a sheet of Cu foil).Typically the former three materials forma separate, discrete anode layer and the latter one forms anotherdiscrete layer.

The most commonly used anode active materials for lithium-ion batteriesare natural graphite and synthetic graphite (or artificial graphite)that can be intercalated with lithium and the resulting graphiteintercalation compound (GIC) may be expressed as Li_(x)C₆, where x istypically less than 1. The maximum amount of lithium that can bereversibly intercalated into the interstices between graphene planes ofa perfect graphite crystal corresponds to x=1, defining a theoreticalspecific capacity of 372 mAh/g.

Graphite or carbon anodes can have a long cycle life due to the presenceof a protective solid-electrolyte interface layer (SEI), which resultsfrom the reaction between lithium and the electrolyte (or betweenlithium and the anode surface/edge atoms or functional groups) duringthe first several charge-discharge cycles. The lithium in this reactioncomes from some of the lithium ions originally intended for the chargetransfer purpose. As the SEI is formed, the lithium ions become part ofthe inert SEI layer and become irreversible, i.e. these positive ionscan no longer be shuttled back and forth between the anode and thecathode during charges/discharges. Therefore, it is desirable to use aminimum amount of lithium for the formation of an effective SEI layer.In addition to SEI formation, the irreversible capacity loss Q_(ir) canalso be attributed to graphite exfoliation caused by electrolyte/solventco-intercalation and other side reactions.

In addition to carbon- or graphite-based anode materials, otherinorganic materials that have been evaluated for potential anodeapplications include metal oxides, metal nitrides, metal sulfides, andthe like, and a range of metals, metal alloys, and intermetalliccompounds that can accommodate lithium atoms/ions or react with lithium.Among these materials, lithium alloys having a composition formula ofLi_(a)A (A is a metal or semiconductor element, such as Al and Si, and“a” satisfies 0<a≤5) are of great interest due to their high theoreticalcapacity, e.g., Li₄Si (3,829 mAh/g), Li_(4.4)Si (4,200 mAh/g),Li_(4. 4)Ge (1,623 mAh/g), Li_(4.4)Sn (993 mAh/g), Li₃Cd (715 mAh/g),Li₃Sb (660 mAh/g), Li_(4.4)Pb (569 mAh/g), LiZn (410 mAh/g), and Li₃Bi(385 mAh/g). However, as schematically illustrated in FIG. 2(A), in ananode composed of these high-capacity materials, severe pulverization(fragmentation of the alloy particles) occurs during the charge anddischarge cycles due to severe expansion and contraction of the anodeactive material particles induced by the insertion and extraction of thelithium ions in and out of these particles. The expansion andcontraction, and the resulting pulverization, of active materialparticles, lead to loss of contacts between active material particlesand conductive additives and loss of contacts between the anode activematerial and its current collector. These adverse effects result in asignificantly shortened charge-discharge cycle life.

To overcome the problems associated with such mechanical degradation,three technical approaches have been proposed:

-   (1) reducing the size of the active material particle, presumably    for the purpose of reducing the total strain energy that can be    stored in a particle, which is a driving force for crack formation    in the particle. However, a reduced particle size implies a higher    surface area available for potentially reacting with the liquid    electrolyte to form a higher amount of SEI. Such a reaction is    undesirable since it is a source of irreversible capacity loss.-   (2) depositing the electrode active material in a thin film form    directly onto a current collector, such as a copper foil. However,    such a thin film structure with an extremely small    thickness-direction dimension (typically much smaller than 500 nm,    often necessarily thinner than 100 nm) implies that only a small    amount of active material can be incorporated in an electrode (given    the same electrode or current collector surface area), providing a    low total lithium storage capacity and low lithium storage capacity    per unit electrode surface area (even though the capacity per unit    mass can be large). Such a thin film must have a thickness less than    100 nm to be more resistant to cycling-induced cracking, further    diminishing the total lithium storage capacity and the lithium    storage capacity per unit electrode surface area. Such a thin-film    battery has very limited scope of application. A desirable and    typical electrode thickness is from 100 μm to 200 μm. These    thin-film electrodes (with a thickness of<500 nm or even<100 nm)    fall short of the required thickness by three (3) orders of    magnitude, not just by a factor of 3.-   (3) using a composite composed of small electrode active particles    protected by (dispersed in or encapsulated by) a less active or    non-active matrix, e.g., carbon-coated Si particles, sol gel    graphite-protected Si, metal oxide-coated Si or Sn, and    monomer-coated Sn nano particles. Presumably, the protective matrix    provides a cushioning effect for particle expansion or shrinkage,    and prevents the electrolyte from contacting and reacting with the    electrode active material. Examples of high-capacity anode active    particles are Si, Sn, and SnO₂.

Unfortunately, when an active material particle, such as Si particle,expands (e.g. up to a volume expansion of 380%) during the batterycharge step, the protective coating is easily broken due to themechanical weakness and/o brittleness of the protective coatingmaterials. There has been no high-strength and high-toughness materialavailable that is itself also lithium ion conductive.

It may be further noted that the coating or matrix materials used toprotect active particles (such as Si and Sn) are carbon, sol gelgraphite, metal oxide, monomer, ceramic, and lithium oxide. Theseprotective materials are all very brittle, weak (of low strength),and/or non-conducting (e.g., ceramic or oxide coating). Ideally, theprotective material should meet the following requirements: (a) Thecoating or matrix material should be of high strength and stiffness sothat it can help to refrain the electrode active material particles,when lithiated, from expanding to an excessive extent. (b) Theprotective material should also have high fracture toughness or highresistance to crack formation to avoid disintegration during repeatedcycling. (c) The protective material must be inert (inactive) withrespect to the electrolyte, but be a good lithium ion conductor. (d) Theprotective material must not provide any significant amount of defectsites that irreversibly trap lithium ions. (e) The protective materialmust be lithium ion-conducting as well as electron-conducting. The priorart protective materials all fall short of these requirements. Hence, itwas not surprising to observe that the resulting anode typically shows areversible specific capacity much lower than expected. In many cases,the first-cycle efficiency is extremely low (mostly lower than 80% andsome even lower than 60%). Furthermore, in most cases, the electrode wasnot capable of operating for a large number of cycles. Additionally,most of these electrodes are not high-rate capable, exhibitingunacceptably low capacity at a high discharge rate.

Due to these and other reasons, most of prior art composite electrodesand electrode active materials have deficiencies in some ways, e.g., inmost cases, less than satisfactory reversible capacity, poor cyclingstability, high irreversible capacity, ineffectiveness in reducing theinternal stress or strain during the lithium ion insertion andextraction steps, and other undesirable side effects.

Complex composite particles of particular interest are a mixture ofseparate Si and graphite particles dispersed in a carbon matrix; e.g.those prepared by Mao, et al. [“Carbon-coated Silicon Particle Powder asthe Anode Material for Lithium Batteries and the Method of Making theSame,” US 2005/0136330 (Jun. 23, 2005)]. Also of interest are carbonmatrix-containing complex nano Si (protected by oxide) and graphiteparticles dispersed therein, and carbon-coated Si particles distributedon a surface of graphite particles Again, these complex compositeparticles led to a low specific capacity or for up to a small number ofcycles only. It appears that carbon by itself is relatively weak andbrittle and the presence of micron-sized graphite particles does notimprove the mechanical integrity of carbon since graphite particles arethemselves relatively weak. Graphite was used in these cases presumablyfor the purpose of improving the electrical conductivity of the anodematerial. Furthermore, polymeric carbon, amorphous carbon, orpre-graphitic carbon may have too many lithium-trapping sites thatirreversibly capture lithium during the first few cycles, resulting inexcessive irreversibility.

In summary, the prior art has not demonstrated a composite material thathas all or most of the properties desired for use as an anode activematerial in a lithium-ion battery. Thus, there is an urgent andcontinuing need for a new anode active material that enables alithium-ion battery to exhibit a high cycle life, high reversiblecapacity, low irreversible capacity, small particle sizes (for high-ratecapacity), and compatibility with commonly used electrolytes. There isalso a need for a method of readily or easily producing such a materialin large quantities.

Thus, it is an object of the present invention to meet these needs andaddress the issues associated the rapid capacity decay of a lithiumbattery containing a high-capacity anode active material.

SUMMARY OF THE INVENTION

Herein reported is an anode active material layer for a lithium batterythat contains a very unique class of anode active materials:high-elasticity polymer-encapsulated or -embraced particles of an anodeactive material that is capable of overcoming the rapid capacity decayproblem commonly associated with a lithium-ion battery that features ahigh-capacity anode active material, such as Si, Sn, and SnO₂.

The anode active material layer comprises multiple particulates of ananode active material, wherein the particulate is composed of one or aplurality of anode active material particles being embraced orencapsulated by a thin layer of a high-elasticity polymer having arecoverable tensile strain no less than 10% (typically 10-700%, moretypically 30-500%, further more typically and desirably>50%, and mostdesirable>100%) when measured without an additive or reinforcement inthe polymer under uniaxial tension, a lithium ion conductivity no lessthan 10⁻⁵ S/cm at room temperature (preferably and more typically noless than 10⁻⁴ S/cm and more preferably and typically no less than 10⁻³S/cm), and a thickness from 0.5 nm (representing a molecular monolayer)to 10 μm. This embracing high-capacity polymer layer preferably has athickness<1 μm, more preferably<100 nm, further more preferably<10 nm,and most preferably from 0.5 nm to 5 nm). The anode active materialpreferably has a specific capacity of lithium storage greater than 372mAh/g, which is the theoretical capacity of graphite.

High-elasticity polymer refers to a polymer, typically a lightlycross-linked polymer, which exhibits an elastic deformation that is atleast 10% when measured (without an additive or reinforcement in thepolymer) under uniaxial tension. In the field of materials science andengineering, the “elastic deformation” is defined as a deformation of amaterial (when being mechanically stressed) that is essentially fullyrecoverable upon release of the load and the recovery is essentiallyinstantaneous. The elastic deformation is preferably greater than 30%,more preferably greater than 50%, further more preferably greater than100%, still more preferably greater than 150%, and most preferablygreater than 200%.

In some preferred embodiments, the high-elasticity polymer contains alightly cross-linked network of polymer chains having an ether linkage,nitrile-derived linkage, benzo peroxide-derived linkage, ethylene oxidelinkage, propylene oxide linkage, vinyl alcohol linkage, cyano-resinlinkage, triacrylate monomer-derived linkage, tetraacrylatemonomer-derived linkage, or a combination thereof, in the cross-linkednetwork of polymer chains. These network or cross-linked polymersexhibit a unique combination of a high elasticity (high elasticdeformation strain) and high lithium-ion conductivity.

In certain preferred embodiments, the high-elasticity polymer contains alightly cross-linked network polymer chains selected fromnitrile-containing polyvinyl alcohol chains, cyanoresin chains,pentaerythritol tetraacrylate (PETEA) chains, pentaerythritoltriacrylate chains, ethoxylated trimethylolpropane triacrylate (ETPTA)chains, ethylene glycol methyl ether acrylate (EGMEA) chains, or acombination thereof.

In this anode active material layer, the anode active material may beselected from the group consisting of: (a) silicon (Si), germanium (Ge),tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum(Al), titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b)alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti,Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides,sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb,Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, orlithium-containing composites; (d) salts and hydroxides of Sn; (e)lithium titanate, lithium manganate, lithium aluminate,lithium-containing titanium oxide, lithium transition metal oxide,ZnCo₂O₄; (f) prelithiated versions thereof; (g) particles of Li, Lialloy, or surface-stabilized Li having at least 60% by weight of lithiumelement therein; and (h) combinations thereof.

In some preferred embodiments, the anode active material contains aprelithiated Si, prelithiated Ge, prelithiated Sn, prelithiated SnO_(x),prelithiated SiO_(x), prelithiated iron oxide, prelithiated VO₂,prelithiated Co₃O₄, prelithiated Ni₃O₄, or a combination thereof,wherein x=1 to 2.

It may be noted that pre-lithiation of an anode active material meansthat this material has been pre-intercalated by or doped with lithiumions up to a weight fraction from 0.1% to 54.7% of Li in the lithiatedproduct.

The anode active material is preferably in a form of nano particle(spherical, ellipsoidal, and irregular shape), nano wire, nano fiber,nano tube, nano sheet, nano belt, nano ribbon, nano disc, nano platelet,or nano horn having a thickness or diameter less than 100 nm. Theseshapes can be collectively referred to as “particles” unless otherwisespecified or unless a specific type among the above species is desired.Further preferably, the anode active material has a dimension less than50 nm, even more preferably less than 20 nm, and most preferably lessthan 10 nm.

In some embodiments, one particle or a cluster of particles may becoated with or embraced by a layer of carbon disposed between theparticle(s) and the high-elasticity polymer layer (the encapsulatingshell). Alternatively or additionally, a carbon layer may be depositedto embrace the encapsulated particle or the encapsulated cluster ofmultiple anode active material particles.

The particulate may further contain a graphite, graphene, or carbonmaterial mixed with the active material particles and disposed insidethe encapsulating or embracing polymer shell. The carbon or graphitematerial is selected from polymeric carbon, amorphous carbon, chemicalvapor deposition carbon, coal tar pitch, petroleum pitch, meso-phasepitch, carbon black, coke, acetylene black, activated carbon, fineexpanded graphite particle with a dimension smaller than 100 nm,artificial graphite particle, natural graphite particle, or acombination thereof. Graphene may be selected from pristine graphene,graphene oxide, reduced graphene oxide, graphene fluoride, hydrogenatedgraphene, nitrogenated graphene, functionalized graphene, etc.

The anode active material particles may be coated with or embraced by aconductive protective coating, selected from a carbon material,graphene, electronically conductive polymer, conductive metal oxide, orconductive metal coating. Preferably, the anode active material, in theform of a nano particle, nano wire, nano fiber, nano tube, nano sheet,nano belt, nano ribbon, nano disc, nano platelet, or nano horn ispre-intercalated or pre-doped with lithium ions to form a prelithiatedanode active material having an amount of lithium from 0.1% to 54.7% byweight of said prelithiated anode active material.

Preferably and typically, the high-elasticity polymer has a lithium ionconductivity no less than 10⁻⁵ S/cm, more preferably no less than 10⁻⁴S/cm, and most preferably no less than 10⁻⁴ S/cm. Some of the selectedpolymers exhibit a lithium-ion conductivity greater than 10⁻² S/cm. Insome embodiments, the high-elasticity polymer is a neat polymercontaining no additive or filler dispersed therein. In others, thehigh-elasticity polymer is polymer matrix composite containing from 0.1%to 50% by weight (preferably from 1% to 35% by weight) of a lithiumion-conducting additive dispersed in a high-elasticity polymer matrixmaterial. In some embodiments, the high-elasticity polymer contains from0.1% by weight to 10% by weight of a reinforcement nano filamentselected from carbon nanotube, carbon nano-fiber, graphene, or acombination thereof.

In some embodiments, the high-elasticity polymer is mixed with anelastomer selected from natural polyisoprene (e.g. cis-1,4-polyisoprenenatural rubber (NR) and trans-1,4-polyisoprene gutta-percha), syntheticpolyisoprene (IR for isoprene rubber), polybutadiene (BR for butadienerubber), chloroprene rubber (CR), polychloroprene (e.g. Neoprene,Baypren etc.), butyl rubber (copolymer of isobutylene and isoprene,IIR), including halogenated butyl rubbers (chloro butyl rubber (CIIR)and bromo butyl rubber (BIIR), styrene-butadiene rubber (copolymer ofstyrene and butadiene, SBR), nitrile rubber (copolymer of butadiene andacrylonitrile, NBR), EPM (ethylene propylene rubber, a copolymer ofethylene and propylene), EPDM rubber (ethylene propylene diene rubber, aterpolymer of ethylene, propylene and a diene-component),epichlorohydrin rubber (ECO), polyacrylic rubber (ACM, ABR), siliconerubber (SI, Q, VMQ), fluorosilicone rubber (FVMQ), fluoroelastomers(FKM, and FEPM; such as Viton, Tecnoflon, Fluorel, Aflas and Dai-El),perfluoroelastomers (FFKM: Tecnoflon PFR, Kalrez, Chemraz, Perlast),polyether block amides (PEBA), chlorosulfonated polyethylene (CSM; e.g.Hypalon), and ethylene-vinyl acetate (EVA), thermoplastic elastomers(TPE), protein resilin, protein elastin, ethylene oxide-epichlorohydrincopolymer, polyurethane, urethane-urea copolymer, and combinationsthereof.

In some embodiments, the high-elasticity polymer is a polymer matrixcomposite containing a lithium ion-conducting additive dispersed in ahigh-elasticity polymer matrix material, wherein the lithiumion-conducting additive is selected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH,LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y),or a combination thereof, wherein X═F, Cl, I, or Br, R=a hydrocarbongroup, x=0−1, y=1−4.

In some embodiments, the high-elasticity polymer is a polymer matrixcomposite containing a lithium ion-conducting additive dispersed in ahigh-elasticity polymer matrix material, wherein the lithiumion-conducting additive contains a lithium salt selected from lithiumperchlorate, LiClO₄, lithium hexafluorophosphate, LiPF₆, lithiumborofluoride, LiBF₄, lithium hexafluoroarsenide, LiAsF₆, lithiumtrifluoro-metasulfonate, LiCF₃SO₃, bis-trifluoromethyl sulfonylimidelithium, LiN(CF₃SO₂)₂, lithium bis(oxalato)borate, LiBOB, lithiumoxalyldifluoroborate, LiBF₂C₂O₄, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-Fluoroalkyl-Phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof.

The high-elasticity polymer may form a mixture or blend with anelectron-conducting polymer selected from polyaniline, polypyrrole,polythiophene, polyfuran, a bi-cyclic polymer, derivatives thereof (e.g.sulfonated versions), or a combination thereof.

In some embodiments, the high-elasticity polymer may form a mixture orblend with a lithium ion-conducting polymer selected from poly(ethyleneoxide) (PEO), Polypropylene oxide (PPO), poly(acrylonitrile) (PAN),poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Polybis-methoxy ethoxyethoxide-phosphazenex, Polyvinyl chloride,Polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene(PVDF-HFP), a sulfonated derivative thereof, or a combination thereof.Sulfonation is herein found to impart improved lithium ion conductivityto a polymer.

The present invention also provides a powder mass of an anode activematerial for a lithium battery, said powder mass comprising multipleparticulates wherein at least a particulate is composed of one or aplurality of particles of a high-capacity anode active material beingencapsulated or embraced by a thin layer of a high-elasticity polymerthat has a recoverable tensile strain (elastic strain) from 10% to 700%,a lithium ion conductivity no less than 10⁻⁵ S/cm at room temperatureand an encapsulating high-elasticity polymer thickness from 0.5 nm to 10μm, and wherein the high-capacity anode active material has a specificcapacity of lithium storage greater than 372 mAh/g. The powder mass mayfurther comprise graphite particles, carbon particles, meso-phasemicrobeads, carbon or graphite fibers, carbon nanotubes, graphenesheets, or a combination thereof. Preferably, the high-capacity anode isprelithiated. In the powder mass, one or a plurality of the anode activematerial particles is coated with a layer of carbon or graphene disposedbetween the one or plurality of particles and the high-elasticitypolymer layer.

The present invention also provides an anode electrode that contains thepresently invented high-elasticity polymer-encapsulated anode materialparticles, an optional conductive additive (e.g. expanded graphiteflakes, carbon black, acetylene black, or carbon nanotube), an optionalresin binder (typically required), and, optionally, some amount of thecommon anode active materials (e.g. particles of natural graphite,synthetic graphite, hard carbon, etc.).

The present invention also provides a lithium battery containing anoptional anode current collector, the presently invented anode activematerial layer as described above, a cathode active material layer, anoptional cathode current collector, an electrolyte in ionic contact withthe anode active material layer and the cathode active material layerand an optional porous separator. The lithium battery may be alithium-ion battery, lithium metal battery (containing lithium metal orlithium alloy as the main anode active material and containing nointercalation-based anode active material), lithium-sulfur battery,lithium-selenium battery, or lithium-air battery.

The present invention also provides a method of manufacturing a lithiumbattery. The method comprises: (a) providing a cathode and an optionalcathode current collector to support the cathode; (b) providing an anodeand an optional anode current collector to support the anode; and (c)providing an electrolyte in contact with the anode and the cathode andan optional separator electrically separating the anode and the cathode;wherein providing the anode includes providing multiple particulates ofan anode active material, wherein a particulate is composed of one or aplurality of anode active material particles being embraced orencapsulated by a thin layer of a high-elasticity polymer having arecoverable tensile strain from 10% to 700% when measured without anadditive or reinforcement, a lithium ion conductivity no less than 10⁻⁵S/cm at room temperature, and a thickness from 0.5 nm to 10 μm.

Preferably, high-elasticity polymer has a thickness from 1 nm to 100 nm.Preferably, the high-elasticity polymer has a lithium ion conductivityfrom 1×10⁻⁵ S/cm to 2×10⁻² S/cm. In some embodiments, thehigh-elasticity polymer has a recoverable tensile strain from 30% to300% (more preferably>50%, and most preferably>100%).

In certain preferred embodiments, the high-elasticity polymer contains across-linked network polymer chains having an ether linkage,nitrile-derived linkage, benzo peroxide-derived linkage, ethylene oxidelinkage, propylene oxide linkage, vinyl alcohol linkage, cyano-resinlinkage, triacrylate monomer-derived linkage, tetraacrylatemonomer-derived linkage, or a combination thereof in the cross-linkednetwork of polymer chains.

Preferably, in the method, the high-elasticity polymer contains across-linked network of polymer chains selected from nitrile-containingpolyvinyl alcohol chains, cyanoresin chains, pentaerythritoltetraacrylate chains, pentaerythritol triacrylate chains, ethoxylatedtrimethylolpropane triacrylate (ETPTA) chains, ethylene glycol methylether acrylate (EGMEA) chains, or a combination thereof.

The step of providing multiple particulates can include encapsulating orembracing the one or a plurality of anode active material particles witha thin layer of high-elasticity polymer using a procedure selected frompan coating, air suspension, centrifugal extrusion, vibrational nozzle,spray-drying, ultrasonic spraying, coacervation-phase separation,interfacial polycondensation, in-situ polymerization, matrixpolymerization, or a combination thereof.

In certain embodiments, the step of providing multiple particulatesincludes encapsulating or embracing said one or a plurality of anodeactive material particles with a mixture of said high-elasticity polymerwith an elastomer, an electronically conductive polymer (e.g.polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer,a sulfonated derivative thereof, or a combination thereof), alithium-ion conducting material, a reinforcement material (e.g. carbonnanotube, carbon nano-fiber, and/or graphene), or a combination thereof.

The lithium ion-conducting material is dispersed in the high-elasticitypolymer and is preferably selected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH,LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y),or a combination thereof, wherein X═F, Cl, I, or Br, R=a hydrocarbongroup, x=0−1, y=1−4.

In some embodiments, the lithium ion-conducting material is dispersed inthe high-elasticity polymer and is selected from lithium perchlorate,LiClO₄, lithium hexafluoro-phosphate, LiPF₆, lithium borofluoride,LiBF₄, lithium hexafluoroarsenide, LiAsF₆, lithiumtrifluoro-metasulfonate, LiCF₃SO₃, bis-trifluoromethyl sulfonylimidelithium, LiN(CF₃SO₂)₂, lithium bis(oxalato)borate, LiBOB, lithiumoxalyldifluoroborate, LiBF₂C₂O₄, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-Fluoroalkyl-Phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof.

In the invented method, the anode active material is selected from thegroup consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), zinc(Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), andcadmium (Cd); (b) oxides, carbides, nitrides, sulfides, phosphides,selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni,Co, V, or Cd, and their mixtures, composites, or lithium-containingcomposites; (c) lithium titanate, lithium manganate, lithium aluminate,lithium-containing titanium oxide, lithium transition metal oxide,ZnCo₂O₄; (d) prelithiated versions thereof; (e) mixtures thereof with acarbon, graphene, or graphite material; (f) particles of Li, Li alloy,or surface-stabilized Li having at least 60% by weight of lithiumelement therein; and (f) combinations thereof.

Preferably, one or a plurality of anode active material particles iscoated with a layer of carbon or graphene disposed between the one orthe plurality of particles and the high-elasticity polymer layer.Preferably, one or a plurality of anode active material particles ismixed with a carbon or graphite material to form a mixture and themixture is embraced by one or a plurality of graphene sheets disposedbetween the mixture and the high-elasticity polymer layer. Preferably,the anode active material particles, possibly along with a carbon orgraphite material and/or with some internal graphene sheets, areembraced by graphene sheets to form anode active material particulates,which are then embraced or encapsulated by the high-elasticity polymer.The graphene sheets may be selected from pristine graphene (e.g. thatprepared by CVD or liquid phase exfoliation using directultrasonication), graphene oxide, reduced graphene oxide (RGO), graphenefluoride, doped graphene, functionalized graphene, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) Schematic of a prior art lithium-ion battery cell, wherein theanode layer is a thin coating of an anode active material itself.

FIG. 1(B) Schematic of another prior art lithium-ion battery; the anodelayer being composed of particles of an anode active material, aconductive additive (not shown) and a resin binder (not shown).

FIG. 2(A) Schematic illustrating the notion that expansion of Siparticles, upon lithium intercalation during charging of a prior artlithium-ion battery, can lead to pulverization of Si particles,interruption of the conductive paths formed by the conductive additive,and loss of contact with the current collector;

FIG. 2(B) illustrates the issues associated with prior art anode activematerial; for instance, a non-lithiated Si particle encapsulated by aprotective shell (e.g. carbon shell) in a core-shell structureinevitably leads to breakage of the shell and that a pre-lithiated Siparticle encapsulated with a protective layer leads to poor contactbetween the contracted Si particle and the rigid protective shell duringbattery discharge.

FIG. 3 Schematic of the presently invented high-elasticitypolymer-encapsulated anode active material particles (pre-lithiated orunlithiated). The high elastic deformation of the polymer shell enablesthe shell to expand and contract congruently and conformingly with thecore particle.

FIG. 4 Schematic of four types of high-elasticity polymer-embraced anodeactive material particles.

FIG. 5(A) The representative tensile stress-strain curves of fourBPO-initiated cross-linked ETPTA polymers.

FIG. 5(B) The specific capacity values of three lithium battery havingan anode active material featuring (1) ETPTA polymer-encapsulated Co₃O₄particles, (2) elastomer-encapsulated Co₃O₄ particles, and (3)un-protected Co₃O₄ particles, respectively.

FIG. 6(A) The representative tensile stress-strain curves of fourPF5-initiated cross-linked PVA-CN polymers.

FIG. 6(B) The specific values of three lithium battery having an anodeactive material featuring (1) high-elasticity polymer-encapsulated SnO₂particles, (2) graphene-wrapped SnO₂ particles, and (3) un-protectedSnO₂ particles, respectively.

FIG. 6(C) The specific values of three lithium battery having an anodeactive material featuring (1) high-elasticity polymer-encapsulated,graphene-wrapped SnO₂ particles, (2) graphene-wrapped SnO₂ particles,and (3) un-protected SnO₂ particles, respectively.

FIG. 7(A) The representative tensile stress-strain curves of threecross-linked PETEA polymers

FIG. 7(B) The discharge capacity curves of four coin cells having fourdifferent types of Sn particulates (protected) or particles(un-protected) as the anode active material: high-elasticitypolymer-encapsulated Sn particles, SBR rubber-encapsulated Sn particles,carbon-encapsulated Sn particles, and un-protected Sn particles.

FIG. 8 Specific capacities of 4 lithium-ion cells having Si nanowires(SiNW) as an anode active material: unprotected SiNW, carbon-coatedSiNW, high-elasticity polymer-encapsulated SiNW, and high-elasticitypolymer-encapsulated carbon-coated SiNW.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is directed at the anode active material layer (negativeelectrode layer, not including the anode current collector) containing ahigh-capacity anode material for a lithium secondary battery, which ispreferably a secondary battery based on a non-aqueous electrolyte, apolymer gel electrolyte, an ionic liquid electrolyte, a quasi-solidelectrolyte, or a solid-state electrolyte. The shape of a lithiumsecondary battery can be cylindrical, square, button-like, etc. Thepresent invention is not limited to any battery shape or configurationor any type of electrolyte. For convenience, we will primarily use Si,Sn, and SnO₂ as illustrative examples of a high-capacity anode activematerial. This should not be construed as limiting the scope of theinvention.

As illustrated in FIG. 1(B), a lithium-ion battery cell is typicallycomposed of an anode current collector (e.g. Cu foil), an anode ornegative electrode active material layer (i.e. anode layer typicallycontaining particles of an anode active material, conductive additive,and binder), a porous separator and/or an electrolyte component, acathode or positive electrode active material layer (containing acathode active material, conductive additive, and resin binder), and acathode current collector (e.g. Al foil). More specifically, the anodelayer is composed of particles of an anode active material (e.g.graphite, Sn, SnO₂, or Si), a conductive additive (e.g. carbon blackparticles), and a resin binder (e.g. SBR or PVDF). This anode layer istypically 50-300 μm thick (more typically 100-200 μm) to give rise to asufficient amount of current per unit electrode area.

In a less commonly used cell configuration, as illustrated in FIG. 1(A),the anode active material is deposited in a thin film form directly ontoan anode current collector, such as a layer of Si coating deposited on asheet of copper foil. This is not commonly used in the battery industryand, hence, will not be discussed further.

In order to obtain a higher energy density cell, the anode in FIG. 1(B)can be designed to contain higher-capacity anode active materials havinga composition formula of Li_(a)A (A is a metal or semiconductor element,such as Al and Si, and “a” satisfies 0<a≤5). These materials are ofgreat interest due to their high theoretical capacity, e.g., Li₄Si(3,829 mAh/g), Li_(4.4)Si (4,200 mAh/g), Li_(4.4)Ge (1,623 mAh/g),Li_(4.4)Sn (993 mAh/g), Li₃Cd (715 mAh/g), Li₃Sb (660 mAh/g), Li_(4.4)Pb(569 mAh/g), LiZn (410 mAh/g), and Li₃Bi (385 mAh/g). However, asdiscussed in the Background section, there are several problemsassociated with the implementation of these high-capacity anode activematerials:

-   1) As schematically illustrated in FIG. 2(A), in an anode composed    of these high-capacity materials, severe pulverization    (fragmentation of the alloy particles) occurs during the charge and    discharge cycles due to severe expansion and contraction of the    anode active material particles induced by the insertion and    extraction of the lithium ions in and out of these particles. The    expansion and contraction, and the resulting pulverization, of    active material particles, lead to loss of contacts between active    material particles and conductive additives and loss of contacts    between the anode active material and its current collector. These    adverse effects result in a significantly shortened charge-discharge    cycle life.-   2) The approach of using a composite composed of small electrode    active particles protected by (dispersed in or encapsulated by) a    less active or non-active matrix, e.g., carbon-coated Si particles,    sol gel graphite-protected Si, metal oxide-coated Si or Sn, and    monomer-coated Sn nano particles, has failed to overcome the    capacity decay problem. Presumably, the protective matrix provides a    cushioning effect for particle expansion or shrinkage, and prevents    the electrolyte from contacting and reacting with the electrode    active material. Unfortunately, when an active material particle,    such as Si particle, expands (e.g. up to a volume expansion of 380%)    during the battery charge step, the protective coating is easily    broken due to the mechanical weakness and/o brittleness of the    protective coating materials. There has been no high-strength and    high-toughness material available that is itself also lithium ion    conductive.-   3) The approach of using a core-shell structure (e.g. Si nano    particle encapsulated in a carbon or SiO₂ shell) also has not solved    the capacity decay issue. As illustrated in upper portion of FIG.    2(B), a non-lithiated Si particle can be encapsulated by a carbon    shell to form a core-shell structure (Si core and carbon or SiO₂    shell in this example). As the lithium-ion battery is charged, the    anode active material (carbon- or SiO₂-encapsulated Si particle) is    intercalated with lithium ions and, hence, the Si particle expands.    Due to the brittleness of the encapsulating shell (carbon), the    shell is broken into segments, exposing the underlying Si to    electrolyte and subjecting the Si to undesirable reactions with    electrolyte during repeated charges/discharges of the battery. These    reactions continue to consume the electrolyte and reduce the cell's    ability to store lithium ions.-   4) Referring to the lower portion of FIG. 2(B), wherein the Si    particle has been pre-lithiated with lithium ions; i.e. has been    pre-expanded in volume. When a layer of carbon (as an example of a    protective material) is encapsulated around the pre-lithiated Si    particle, another core-shell structure is formed. However, when the    battery is discharged and lithium ions are released    (de-intercalated) from the Si particle, the Si particle contracts,    leaving behind a large gap between the protective shell and the Si    particle. Such a configuration is not conducive to lithium    intercalation of the Si particle during the subsequent battery    charge cycle due to the gap and the poor contact of Si particle with    the protective shell (through which lithium ions can diffuse). This    would significantly curtail the lithium storage capacity of the Si    particle particularly under high charge rate conditions.

In other words, there are several conflicting factors that must beconsidered concurrently when it comes to the design and selection of ananode active material in terms of material type, shape, size, porosity,and electrode layer thickness. Thus far, there has been no effectivesolution offered by any prior art teaching to these often conflictingproblems. We have solved these challenging issues that have troubledbattery designers and electrochemists alike for more than 30 years bydeveloping the elastomer-protected anode active material.

The anode active material layer comprises multiple particulates of ananode active material, wherein the particulate is composed of one or aplurality of anode active material particles being embraced orencapsulated by a thin layer of a high-elasticity polymer having arecoverable tensile strain no less than 10% when measured without anadditive or reinforcement in the polymer under uniaxial tension, alithium ion conductivity no less than 10⁻⁵ S/cm at room temperature(preferably and more typically no less than 10⁻⁴ S/cm and morepreferably and typically no less than 10⁻³ S/cm), and a thickness from0.5 nm (representing a molecular monolayer) to 10 μm. This embracinghigh-capacity polymer layer preferably has a thickness<1 μm, morepreferably<100 nm, further more preferably<10 nm, and most preferablyfrom 0.5 nm to 5 nm). The anode active material preferably has aspecific capacity of lithium storage greater than 372 mAh/g, which isthe theoretical capacity of graphite.

High-elasticity polymer refers to a polymer, typically a lightlycross-linked polymer, which exhibits an elastic deformation that is atleast 10% when measured (without an additive or reinforcement in thepolymer) under uniaxial tension. In the field of materials science andengineering, the “elastic deformation” is defined as a deformation of amaterial (when being mechanically stressed) that is essentially fullyrecoverable and the recovery is essentially instantaneous upon releaseof the load. The elastic deformation is preferably greater than 30%,more preferably greater than 50%, further more preferably greater than100%, still more preferably greater than 150%, and most preferablygreater than 200%. The preferred types of high-capacity polymers will bediscussed later.

As illustrated in FIG. 4, the present invention provides four majortypes of particulates of high-capacity polymer-encapsulated anode activematerial particles. The first one is a single-particle particulatecontaining an anode active material core 10 encapsulated by ahigh-capacity polymer shell 12. The second is a multiple-particleparticulate containing multiple anode active material particles 14 (e.g.Si nano particles), optionally along with other active materials (e.g.particles of graphite or hard carbon, not shown) or conductive additive,which are encapsulated by a high-capacity polymer 16. The third is asingle-particle particulate containing an anode active material core 18coated by a carbon or graphene layer 20 (or other conductive material)further encapsulated by a high-elasticity polymer 22. The fourth is amultiple-particle particulate containing multiple anode active materialparticles 24 (e.g. Si nano particles) coated with a conductiveprotection layer 26 (carbon, graphene, etc.), optionally along withother active materials (e.g. particles of graphite or hard carbon, notshown) or conductive additive, which are encapsulated by ahigh-elasticity polymer shell 28. These anode active material particlescan be pre-lithiated or non-prelithiated.

As schematically illustrated in the upper portion of FIG. 3, anon-lithiated Si particle can be encapsulated by a high-capacity polymershell to form a core-shell structure (Si core and polymer shell in thisexample). As the lithium-ion battery is charged, the anode activematerial (high-capacity polymer-encapsulated Si particle) isintercalated with lithium ions and, hence, the Si particle expands. Dueto the high elasticity of the encapsulating shell (the high-capacitypolymer), the shell will not be broken into segments (in contrast to thebroken carbon shell). That the high-capacity polymer shell remainsintact prevents the exposure of the underlying Si to electrolyte and,thus, prevents the Si from undergoing undesirable reactions withelectrolyte during repeated charges/discharges of the battery. Thisstrategy prevents continued consumption of the electrolyte to formadditional SEI.

Alternatively, referring to the lower portion of FIG. 3, wherein the Siparticle has been pre-lithiated with lithium ions; i.e. has beenpre-expanded in volume. When a layer of high-capacity polymer isencapsulated around the pre-lithiated Si particle, another core-shellstructure is formed. When the battery is discharged and lithium ions arereleased (de-intercalated) from the Si particle, the Si particlecontracts. However, the high-capacity polymer is capable of elasticallyshrinking in a conformal manner; hence, leaving behind no gap betweenthe protective shell and the Si particle. Such a configuration isamenable to subsequent lithium intercalation and de-intercalation of theSi particle. The high-capacity polymer shell expands and shrinkscongruently with the expansion and shrinkage of the encapsulated coreanode active material particle, enabling long-term cycling stability ofa lithium battery featuring a high-capacity anode active material (suchas Si, Sn, SnO₂, Co₃O₄, etc.).

The anode active material may be selected from the group consisting of:(a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb),bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni),cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds ofSi, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements;(c) oxides, carbides, nitrides, sulfides, phosphides, selenides, andtellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd,and their mixtures, composites, or lithium-containing composites; (d)salts and hydroxides of Sn; (e) lithium titanate, lithium manganate,lithium aluminate, lithium-containing titanium oxide, lithium transitionmetal oxide, ZnCo₂O₄; (f) prelithiated versions thereof; (g) particlesof Li, Li alloy, or surface-stabilized Li; and (h) combinations thereof.Particles of Li or Li alloy (Li alloy containing from 0.1% to 10% byweight of Zn, Ag, Au, Mg, Ni, Ti, Fe, Co, or V element), particularlysurface-stabilized Li particles (e.g. wax-coated Li particles), werefound to be good anode active material per se or an extra lithium sourceto compensate for the loss of Li ions that are otherwise supplied onlyfrom the cathode active material. The presence of these Li or Li-alloyparticles encapsulated inside an elastomeric shell was found tosignificantly improve the cycling performance of a lithium cell.

Pre-lithiation of an anode active material can be conducted by severalmethods (chemical intercalation, ion implementation, and electrochemicalintercalation). Among these, the electrochemical intercalation is themost effective. Lithium ions can be intercalated into non-Li elements(e.g. Si, Ge, and Sn) and compounds (e.g. SnO₂ and Co₃O₄) up to a weightpercentage of 54.68% (see Table 1 below). For Zn, Mg, Ag, and Auencapsulated inside an elastomer shell, the amount of Li can reach 99%by weight.

TABLE 1 Lithium storage capacity of selected non-Li elements.Intercalated Atomic weight Atomic weight of Max. wt. % compound of Li,g/mole active material, g/mole of Li Li₄Si 6.941 28.086 49.71 Li_(4.4)Si6.941 28.086 54.68 Li_(4.4)Ge 6.941 72.61 30.43 Li4.4Sn 6.941 118.7120.85 Li₃Cd 6.941 112.411 14.86 Li₃Sb 6.941 121.76 13.93 Li_(4.4)Pb6.941 207.2 13.00 LiZn 6.941 65.39 7.45 Li₃Bi 6.941 208.98 8.80

The particles of the anode active material may be in the form of a nanoparticle, nano wire, nano fiber, nano tube, nano sheet, nano platelet,nano disc, nano belt, nano ribbon, or nano horn. They can benon-lithiated (when incorporated into the anode active material layer)or pre-lithiated to a desired extent (up to the maximum capacity asallowed for a specific element or compound.

Preferably and typically, the high-capacity polymer has a lithium ionconductivity no less than 10⁻⁵ S/cm, more preferably no less than 10⁻⁴S/cm, further preferably no less than 10⁻³ S/cm, and most preferably noless than 10⁻² S/cm. In some embodiments, the high-capacity polymer is aneat polymer having no additive or filler dispersed therein. In others,the high-capacity polymer is a polymer matrix composite containing from0.1% to 50% (preferably 1% to 35%) by weight of a lithium ion-conductingadditive dispersed in a high-capacity polymer matrix material. Thehigh-capacity polymer must have a high elasticity (elastic deformationstrain value>10%). An elastic deformation is a deformation that is fullyrecoverable and the recovery process is essentially instantaneous (nosignificant time delay). The high-capacity polymer can exhibit anelastic deformation from 10% up to 1,000% (10 times of its originallength), more typically from 10% to 800%, and further more typicallyfrom 50% to 500%, and most typically and desirably from 70% to 300%. Itmay be noted that although a metal typically has a high ductility (i.e.can be extended to a large extent without breakage), the majority of thedeformation is plastic deformation (non-recoverable) and only a smallamount of elastic deformation (typically<1% and more typically<0.2%).

In some preferred embodiments, the high-elasticity polymer contains alightly cross-linked network polymer chains having an ether linkage,nitrile-derived linkage, benzo peroxide-derived linkage, ethylene oxidelinkage, propylene oxide linkage, vinyl alcohol linkage, cyano-resinlinkage, triacrylate monomer-derived linkage, tetraacrylatemonomer-derived linkage, or a combination thereof, in the cross-linkednetwork of polymer chains. These network or cross-linked polymersexhibit a unique combination of a high elasticity (high elasticdeformation strain) and high lithium-ion conductivity.

In certain preferred embodiments, the high-elasticity polymer contains alightly cross-linked network polymer chains selected fromnitrile-containing polyvinyl alcohol chains, cyanoresin chains,pentaerythritol tetraacrylate (PETEA) chains, pentaerythritoltriacrylate chains, ethoxylated trimethylolpropane triacrylate (ETPTA)chains, ethylene glycol methyl ether acrylate (EGMEA) chains, or acombination thereof.

Typically, a high-elasticity polymer is originally in a monomer oroligomer states that can be cured to form a cross-linked polymer that ishighly elastic. Prior to curing, these polymers or oligomers are solublein an organic solvent to form a polymer solution. Particles of an anodeactive material (e.g. SnO₂ nano particles and Si nano-wires) can bedispersed in this polymer solution to form a suspension (dispersion orslurry) of an active material particle-polymer (monomer or oligomer)mixture. This suspension can then be subjected to a solvent removaltreatment while individual particles remain substantially separated fromone another. The polymer (or monomer or oligomer) precipitates out todeposit on surfaces of these active material particles. This can beaccomplished, for instance, via spray drying, ultrasonic spraying,air-assisted spraying, aerosolization, and other secondary particleformation procedures.

For instance, ethoxylated trimethylopropane triacrylate monomer (ETPTA,Mw=428, chemical formula given below), along with an initiator, can bedissolved in an organic solvent, such as ethylene carbonate (EC) ordiethyl carbonate (DEC). Then, anode active material particles (Si, Sn,SnO₂, and Co₃O₄ particles, etc.) can be dispersed in the ETPTAmonomer/solvent/initiator solution to form a slurry, which can bespray-dried to form ETPTA monomer/initiator-embraced anode particles.These embraced particles can then be thermally cured to obtain theparticulates composed of anode particles encapsulated with a thin layerof a high-elasticity polymer. The polymerization and cross-linkingreactions of this monomer can be initiated by a radical initiatorderived from benzoyl peroxide (BPO) or AIBN through thermaldecomposition of the initiator molecule. The ETPTA monomer has thefollowing chemical formula:

As another example, the high-elasticity polymer for encapsulation maybes based on cationic polymerization and cross-linking of the cyanoethylpolyvinyl alcohol (PVA-CN, Formula 2) in succinonitrile (SN).

The procedure may begin with dissolving PVA-CN in succinonitrile(NCCH₂CH₂CN) to form a mixture solution. This is followed by adding aninitiator into the mixture solution. For instance, LiPF₆ can be addedinto the PVA-CN/SN mixture solution at a weight ratio (selected from thepreferred range from 20:1 to 2:1) to form a precursor solution. Then,particles of a selected anode active material are introduced into themixture solution to form a slurry. The slurry may then be subjected to amicro-encapsulation procedure to produce anode active material particlescoated with an embracing layer of reacting mass, PVA-CN/LiPF₆. Theseembraced particles can then be heated at a temperature (e.g. from 75 to100° C.) for 2 to 8 hours to obtain high-elasticity polymer-encapsulatedanode active material particles. During this process, cationicpolymerization and cross-linking of cyano groups on the PVA-CN may beinitiated by PF₅, which is derived from the thermal decomposition ofLiPF₆ at such an elevated temperature.

It is essential for these materials to form a lightly cross-linkednetwork of polymer chains. In other words, the network polymer orcross-linked polymer should have a relatively low degree ofcross-linking or low cross-link density to impart a high elasticdeformation.

The cross-link density of a cross-linked network of polymer chains maybe defined as the inverse of the molecular weight between cross-links(Mc). The cross-link density can be determined by the equation,Mc=ρRT/Ge, where Ge is the equilibrium modulus as deter mined by atemperature sweep in dynamic mechanical analysis, ρ is the physicaldensity, R is the universal gas constant in J/mol*K and T is absolutetemperature in K. Once Ge and ρ are determined experimentally, then Mcand the cross-link density can be calculated.

The magnitude of Mc may be normalized by dividing the Mc value by themolecular weight of the characteristic repeat unit in the cross-linkchain or chain linkage to obtain a number, Nc, which is the number ofrepeating units between two cross-link points. We have found that theelastic deformation strain correlates very well with Mc and Nc. Theelasticity of a cross-linked polymer derives from a large number ofrepeating units (large Nc) between cross-links. The repeating units canassume a more relax conformation (e.g. random coil) when the polymer isnot stressed. However, when the polymer is mechanically stressed, thelinkage chain uncoils or gets stretched to provide a large deformation.A long chain linkage between cross-link points (larger Nc) enables alarger elastic deformation. Upon release of the load, the linkage chainreturns to the more relaxed or coiled state. During mechanical loadingof a polymer, the cross-links prevent slippage of chains that otherwiseform plastic deformation (non-recoverable).

Preferably, the Nc value in a high-elasticity polymer is greater than 5,more preferably greater than 10, further more preferably greater than100, and even more preferably greater than 200. These Nc values can bereadily controlled and varied to achieve different elastic deformationvalues by using different cross-linking agents with differentfunctionalities, and by designing the polymerization and cross-linkingreactions to proceed at different temperatures for different periods oftime.

Alternatively, Mooney-Rilvin method may be used to determine the degreeof cross-linking. Crosslinking also can be measured by swellingexperiments. In a swelling experiment, the crosslinked sample is placedinto a good solvent for the corresponding linear polymer at a specifictemperature, and either the change in mass or the change in volume ismeasured. The higher the degree of crosslinking, the less swelling isattainable. Based on the degree of swelling, the Flory InteractionParameter (which relates the solvent interaction with the sample, FloryHuggins Eq.), and the density of the solvent, the theoretical degree ofcrosslinking can be calculated according to Flory's Network Theory. TheFlory-Rehner Equation can be useful in the determination ofcross-linking.

The high-elasticity polymer for encapsulation may contain a simultaneousinterpenetrating network (SIN) polymer, wherein two cross-linking chainsintertwine with each other, or a semi-interpenetrating network polymer(semi-IPN), which contains a cross-linked polymer and a linear polymer.An example of semi-IPN is an UV-curable/polymerizabletrivalent/monovalent acrylate mixture, which is composed of ethoxylatedtrimethylolpropane triacrylate (ETPTA) and ethylene glycol methyl etheracrylate (EGMEA) oligomers. The ETPTA, bearing trivalent vinyl groups,is a photo (UV)-crosslinkable monomer, capable of forming a network ofcross-linked chains. The EGMEA, bearing monovalent vinyl groups, is alsoUV-polymerizable, leading to a linear polymer with a high flexibilitydue to the presence of the oligomer ethylene oxide units. When thedegree of cross-linking of ETPTA is moderate or low, the resultingETPTA/EGMEA semi-IPN polymer provides good mechanical flexibility orelasticity and reasonable mechanical strength. The lithium-ionconductivity of this polymer is in the range of 10⁻⁴ to 5×10⁻³ S/cm.

The aforementioned high-elasticity polymers may be used alone to embraceor encapsulate anode active material particles. Alternatively, thehigh-elasticity polymer can be mixed with a broad array of elastomers,electrically conducting polymers, lithium ion-conducting materials,and/or strengthening materials (e.g. carbon nanotube, carbon nano-fiber,or graphene sheets).

A broad array of elastomers can be mixed with a high-elasticity polymerto encapsulate or embrace an anode active material particle or multipleparticles. Encapsulation means substantially fully embracing theparticle(s) without allowing the particle(s) to be in direct contactwith electrolyte in the battery when the high-elasticity polymer isimplemented in the anode of an actual battery. The elastomeric materialmay be selected from natural polyisoprene (e.g. cis-1,4-polyisoprenenatural rubber (NR) and trans-1,4-polyisoprene gutta-percha), syntheticpolyisoprene (IR for isoprene rubber), polybutadiene (BR for butadienerubber), chloroprene rubber (CR), polychloroprene (e.g. Neoprene,Baypren etc.), butyl rubber (copolymer of isobutylene and isoprene,IIR), including halogenated butyl rubbers (chloro butyl rubber (CIIR)and bromo butyl rubber (BIIR), styrene-butadiene rubber (copolymer ofstyrene and butadiene, SBR), nitrile rubber (copolymer of butadiene andacrylonitrile, NBR), EPM (ethylene propylene rubber, a copolymer ofethylene and propylene), EPDM rubber (ethylene propylene diene rubber, aterpolymer of ethylene, propylene and a diene-component),epichlorohydrin rubber (ECO), polyacrylic rubber (ACM, ABR), siliconerubber (SI, Q, VMQ), fluorosilicone rubber (FVMQ), fluoroelastomers(FKM, and FEPM; such as Viton, Tecnoflon, Fluorel, Aflas and Dai-El),perfluoroelastomers (FFKM: Tecnoflon PFR, Kalrez, Chemraz, Perlast),polyether block amides (PEBA), chlorosulfonated polyethylene (CSM; e.g.Hypalon), and ethylene-vinyl acetate (EVA), thermoplastic elastomers(TPE), protein resilin, protein elastin, ethylene oxide-epichlorohydrincopolymer, polyurethane, urethane-urea copolymer, and combinationsthereof.

The urethane-urea copolymer film usually consists of two types ofdomains, soft domains and hard ones. Entangled linear backbone chainsconsisting of poly(tetramethylene ether) glycol (PTMEG) units constitutethe soft domains, while repeated methylene diphenyl diisocyanate (MDI)and ethylene diamine (EDA) units constitute the hard domains. Thelithium ion-conducting additive can be incorporated in the soft domainsor other more amorphous zones.

In some embodiments, a high-elasticity polymer can form a polymer matrixcomposite containing a lithium ion-conducting additive dispersed in thehigh-elasticity polymer matrix material, wherein the lithiumion-conducting additive is selected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH,LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y),or a combination thereof, wherein X═F, Cl, I, or Br, R=a hydrocarbongroup, x=0−1, y=1−4.

In some embodiments, the high-elasticity polymer can be mixed with alithium ion-conducting additive, which contains a lithium salt selectedfrom lithium perchlorate, LiClO₄, lithium hexafluorophosphate, LiPF₆,lithium borofluoride, LiBF₄, lithium hexafluoroarsenide, LiAsF₆, lithiumtrifluoro-metasulfonate, LiCF₃ SO₃, bis-trifluoromethyl sulfonylimidelithium, LiN(CF₃SO₂)₂, lithium bis(oxalato)borate, LiBOB, lithiumoxalyldifluoroborate, LiBF₂C₂O₄, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-Fluoroalkyl-Phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof.

The high-elasticity polymer may form a mixture or blend with anelectron-conducting polymer selected from polyaniline, polypyrrole,polythiophene, polyfuran, a bi-cyclic polymer, derivatives thereof (e.g.sulfonated versions), or a combination thereof.

In some embodiments, the high-elasticity polymer may form a mixture orwith a lithium ion-conducting polymer selected from poly(ethylene oxide)(PEO), Polypropylene oxide (PPO), poly(acrylonitrile) (PAN), poly(methylmethacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a derivativethereof (e.g. sulfonated versions), or a combination thereof.

Unsaturated rubbers that can be vulcanized to become elastomer includenatural polyisoprene (e.g. cis-1,4-polyisoprene natural rubber (NR) andtrans-1,4-polyisoprene gutta-percha), synthetic polyisoprene (IR forisoprene rubber), polybutadiene (BR for butadiene rubber), chloroprenerubber (CR), polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber(copolymer of isobutylene and isoprene, IIR), including halogenatedbutyl rubbers (chloro butyl rubber (CIIR) and bromo butyl rubber (BIIR),styrene-butadiene rubber (copolymer of styrene and butadiene, SBR),nitrile rubber (copolymer of butadiene and acrylonitrile, NBR),

Some elastomers are saturated rubbers that cannot be cured by sulfurvulcanization; they are made into a rubbery or elastomeric material viadifferent means: e.g. by having a copolymer domain that holds otherlinear chains together. Each of these elastomers can be used toencapsulate particles of an anode active material by one of severalmeans: melt mixing (followed by pelletizing and ball-milling, forinstance), solution mixing (dissolving the anode active materialparticles in an uncured polymer, monomer, or oligomer, with or withoutan organic solvent) followed by drying (e.g. spray drying), interfacialpolymerization, or in situ polymerization of elastomer in the presenceof anode active material particles.

Saturated rubbers and related elastomers in this category include EPM(ethylene propylene rubber, a copolymer of ethylene and propylene), EPDMrubber (ethylene propylene diene rubber, a terpolymer of ethylene,propylene and a diene-component), epichlorohydrin rubber (ECO),polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ),fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such asViton, Tecnoflon, Fluorel, Aflas and Dai-El), perfluoroelastomers (FFKM:Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA),chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinylacetate (EVA), thermoplastic elastomers (TPE), protein resilin, andprotein elastin. Polyurethane and its copolymers (e.g. urea-urethanecopolymer) are particularly useful elastomeric shell materials forencapsulating anode active material particles.

Several micro-encapsulation processes require the high-elasticitypolymer or its precursor (monomer or oligomer) to be dissolvable in asolvent. Fortunately, all the high-elasticity polymers or theirprecursors used herein are soluble in some common solvents. The un-curedpolymer or its precursor can be readily dissolved in a common organicsolvent to form a solution. This solution can then be used toencapsulate solid particles via several of the micro-encapsulationmethods to be discussed in what follows. Upon encapsulation, the polymershell is then polymerized and cross-linked.

There are three broad categories of micro-encapsulation methods that canbe implemented to produce high-elasticity polymer-encapsulated particlesof an anode active material: physical methods, physico-chemical methods,and chemical methods. The physical methods include pan-coating,air-suspension coating, centrifugal extrusion, vibration nozzle, andspray-drying methods. The physico-chemical methods include ionotropicgelation and coacervation-phase separation methods. The chemical methodsinclude interfacial polycondensation, interfacial cross-linking, in-situpolymerization, and matrix polymerization.

Pan-coating method: The pan coating process involves tumbling the activematerial particles in a pan or a similar device while the encapsulatingmaterial (e.g. monomer/oligomer, polymer melt, polymer/solvent solution)is applied slowly until a desired encapsulating shell thickness isattained.

Air-suspension coating method: In the air suspension coating process,the solid particles (core material) are dispersed into the supportingair stream in an encapsulating chamber. A controlled stream of apolymer-solvent solution (polymer or its monomer or oligomer dissolvedin a solvent; or its monomer or oligomer alone in a liquid state) isconcurrently introduced into this chamber, allowing the solution to hitand coat the suspended particles. These suspended particles areencapsulated (fully coated) with a polymer or its precursor moleculeswhile the volatile solvent is removed, leaving a very thin layer ofpolymer (or its precursor, which is cured/hardened subsequently) onsurfaces of these particles. This process may be repeated several timesuntil the required parameters, such as full-coating thickness (i.e.encapsulating shell or wall thickness), are achieved. The air streamwhich supports the particles also helps to dry them, and the rate ofdrying is directly proportional to the temperature of the air stream,which can be adjusted for optimized shell thickness.

In a preferred mode, the particles in the encapsulating zone portion maybe subjected to re-circulation for repeated coating. Preferably, theencapsulating chamber is arranged such that the particles pass upwardsthrough the encapsulating zone, then are dispersed into slower movingair and sink back to the base of the encapsulating chamber, enablingrepeated passes of the particles through the encapsulating zone untilthe desired encapsulating shell thickness is achieved.

Centrifugal extrusion: Anode active materials may be encapsulated usinga rotating extrusion head containing concentric nozzles. In thisprocess, a stream of core fluid (slurry containing particles of an anodeactive material dispersed in a solvent) is surrounded by a sheath ofshell solution or melt. As the device rotates and the stream movesthrough the air it breaks, due to Rayleigh instability, into droplets ofcore, each coated with the shell solution. While the droplets are inflight, the molten shell may be hardened or the solvent may beevaporated from the shell solution. If needed, the capsules can behardened after formation by catching them in a hardening bath. Since thedrops are formed by the breakup of a liquid stream, the process is onlysuitable for liquid or slurry. A high production rate can be achieved.Up to 22.5 kg of microcapsules can be produced per nozzle per hour andextrusion heads containing 16 nozzles are readily available.

Vibrational nozzle method: Core-shell encapsulation ormatrix-encapsulation of an anode active material can be conducted usinga laminar flow through a nozzle and vibration of the nozzle or theliquid. The vibration has to be done in resonance with the Rayleighinstability, leading to very uniform droplets. The liquid can consist ofany liquids with limited viscosities (1-50,000 mPa·s): emulsions,suspensions or slurry containing the anode active material. Thesolidification can be done according to the used gelation system with aninternal gelation (e.g. sol-gel processing, melt) or an external(additional binder system, e.g. in a slurry).

Spray-drying: Spray drying may be used to encapsulate particles of anactive material when the active material is dissolved or suspended in amelt or polymer solution. In spray drying, the liquid feed (solution orsuspension) is atomized to form droplets which, upon contacts with hotgas, allow solvent to get vaporized and thin polymer shell to fullyembrace the solid particles of the active material.

Coacervation-phase separation: This process consists of three stepscarried out under continuous agitation:

-   (a) Formation of three immiscible chemical phases: liquid    manufacturing vehicle phase, core material phase and encapsulation    material phase. The core material is dispersed in a solution of the    encapsulating polymer (or its monomer or oligomer). The    encapsulating material phase, which is an immiscible polymer in    liquid state, is formed by (i) changing temperature in polymer    solution, (ii) addition of salt, (iii) addition of non-solvent,    or (iv) addition of an incompatible polymer in the polymer solution.-   (b) Deposition of encapsulation shell material: core material being    dispersed in the encapsulating polymer solution, encapsulating    polymer material coated around core particles, and deposition of    liquid polymer embracing around core particles by polymer adsorbed    at the interface formed between core material and vehicle phase; and-   (c) Hardening of encapsulating shell material: shell material being    immiscible in vehicle phase and made rigid via thermal,    cross-linking, or dissolution techniques.

Interfacial polycondensation and interfacial cross-linking: Interfacialpolycondensation entails introducing the two reactants to meet at theinterface where they react with each other. This is based on the conceptof the Schotten-Baumann reaction between an acid chloride and a compoundcontaining an active hydrogen atom (such as an amine or alcohol),polyester, polyurea, polyurethane, or urea-urethane condensation. Underproper conditions, thin flexible encapsulating shell (wall) formsrapidly at the interface. A solution of the anode active material and adiacid chloride are emulsified in water and an aqueous solutioncontaining an amine and a polyfunctional isocyanate is added. A base maybe added to neutralize the acid formed during the reaction. Condensedpolymer shells form instantaneously at the interface of the emulsiondroplets. Interfacial cross-linking is derived from interfacialpolycondensation, wherein cross-linking occurs between growing polymerchains and a multi-functional chemical groups to form an elastomer shellmaterial.

In-situ polymerization: In some micro-encapsulation processes, activematerials particles are fully coated with a monomer or oligomer first.Then, direct polymerization and cross-linking of the monomer or oligomeris carried out on the surfaces of these material particles.

Matrix polymerization: This method involves dispersing and embedding acore material in a polymeric matrix during formation of the particles.This can be accomplished via spray-drying, in which the particles areformed by evaporation of the solvent from the matrix material. Anotherpossible route is the notion that the solidification of the matrix iscaused by a chemical change.

EXAMPLE 1 High-Elasticity Polymer-Protected Cobalt Oxide (Co₃O₄) AnodeParticulates

An appropriate amount of inorganic salts Co(NO₃)₂·6H₂O and ammoniasolution (NH₃·H₂O, 25 wt. %) were mixed together. The resultingsuspension was stirred for several hours under an argon flow to ensure acomplete reaction. The obtained Co(OH)₂ precursor suspension wascalcined at 450° C. in air for 2 h to form particles of the layeredCo₃O₄. Portion of the Co₃O₄ particles was then encapsulated with anETPTA-based high-elasticity polymer according to the followingprocedure:

The ethoxylated trimethylopropane triacrylate monomer (ETPTA, Mw=428,Sigma-Aldrich) was dissolved in a solvent mixture of ethylene carbonate(EC)/diethyl carbonate (DEC), at a weight-based composition ratios ofthe ETPTA/solvent of 3/97 (w/w). Subsequently, benzoyl peroxide (BPO,1.0 wt. % relative to the ETPTA content) was added as a radicalinitiator to allow for thermal crosslinking reaction after mixing withanode particles. Then, anode active material particles (Co₃O₄ particles)were dispersed in the ETPTA monomer/solvent/initiator solution to form aslurry, which was spray-dried to form ETPTA monomer/initiator-embracedCo₃O₄ particles. These embraced particles were then thermally cured at60° C. for 30 min. to obtain the particulates composed of Co₃O₄particles encapsulated with a thin layer of a high-elasticity polymermonomer has the following chemical formula:

The ETPTA polymer shell thickness was varied from 2.7 nm to 121 nm.

On a separate basis, some amount of the ETPTA monomer/solvent/initiatorsolution was cast onto a glass surface to form a wet film, which wasthermally dried and then cured at 60° C. for 30 min to form a film ofcross-linked polymer. In this experiment, the BPO/ETPTA weight ratio wasvaried from 0.1% to 4% to vary the degree of cross-linking in severaldifferent polymer films. Some of the cure polymer samples were subjectedto dynamic mechanical testing to obtain the equilibrium dynamic modulus,Ge, for the determination of the number average molecular weight betweentwo cross-link points (Mc) and the corresponding number of repeat units(Nc), as a means of characterizing the degree of cross-linking.

Several tensile testing specimens were cut from each cross-link film andtested with a universal testing machine. The representative tensilestress-strain curves of four BPO-initiated cross-linked ETPTA polymersare shown in FIG. 5(A), which indicate that this series of networkpolymers have an elastic deformation from approximately 230% to 700%.These above are for neat polymers without any additive. The addition ofup to 30% by weight of a lithium salt typically reduces this elasticitydown to a reversible tensile strain from 10% to 100%.

For electrochemical testing, the working electrodes were prepared bymixing 85 wt. % active material (encapsulated or non-encapsulatedparticulates of Co₃O₄, separately), 7 wt. % acetylene black (Super-P),and 8 wt. % polyvinylidene fluoride (PVDF) binder dissolved inN-methyl-2-pyrrolidinoe (NMP) to form a slurry of 5 wt. % total solidcontent. After coating the slurries on Cu foil, the electrodes weredried at 120° C. in vacuum for 2 h to remove the solvent beforepressing. Then, the electrodes were cut into a disk (ϕ=12 mm) and driedat 100° C. for 24 h in vacuum. Electrochemical measurements were carriedout using CR2032 (3V) coin-type cells with lithium metal as thecounter/reference electrode, Celgard 2400 membrane as separator, and 1 MLiPF₆ electrolyte solution dissolved in a mixture of ethylene carbonate(EC) and diethyl carbonate (DEC) (EC-DEC, 1:1 v/v). The cell assemblywas performed in an argon-filled glove-box. The CV measurements werecarried out using a CH-6 electrochemical workstation at a scanning rateof 1 mV/s.

The electrochemical performance of the particulates of high-elasticitypolymer-encapsulated Co₃O₄ particles, elastomer-encapsulated Co₃O₄particles and non-protected Co₃O₄ particles were evaluated bygalvanostatic charge/discharge cycling at a current density of 50 mA/g,using a LAND electrochemical workstation. The results indicate that thecharge/discharge profiles for the encapsulated Co₃O₄ particles andun-protected Co₃O₄ particle-based electrodes show a long voltage plateauat about 1.06 V and 1.10 V, respectively, followed by a slopping curvedown to the cut-off voltage of 0.01 V, indicative of typicalcharacteristics of voltage trends for the Co₃O₄ electrode.

As summarized in FIG. 5(B), the first-cycle lithium insertion capacityvalues are 752 mAh/g (non-encapsulated), 751 mAh/g (urea-urethanecopolymer-encapsulated), and 752 mAh/g (BPO-initiated ETPTApolymer-encapsulated), respectively, which are higher than thetheoretical values of graphite (372 mAh/g). All cells exhibit somefirst-cycle irreversibility. The initial capacity loss might haveresulted from the incomplete conversion reaction and partiallyirreversible lithium loss due to the formation of solid electrolyteinterface (SET) layers.

As the number of cycles increases, the specific capacity of the bareCo₃O₄ electrode drops precipitously. Compared with its initial capacityvalue of approximately 752 mAh/g, its capacity suffers a 20% loss after150 cycles and a 40.16% loss after 260 cycles. The urea-urethanecopolymer-encapsulated particulates provide the battery cell with a verystable and high specific capacity for a large number of cycles,experiencing a capacity loss of 3.33% after 260 cycles. The presentlyinvented high-elasticity polymer-encapsulated particulates provide thebattery cell with the most stable and high specific capacity for a largenumber of cycles, experiencing a capacity loss of 2.53% after 260cycles. Furthermore, the BPO-initiated ETPTA polymer exhibits a lithiumion conductivity that is 2 orders of magnitude higher than that of theurea-urethane elastomer, leading to a higher rate capability of thebattery featuring the instant anode. These data have clearlydemonstrated the surprising and superior performance of the presentlyinvented particulate electrode materials compared with prior artun-encapsulated particulate-based electrode materials.

It may be noted that the number of charge-discharge cycles at which thespecific capacity decays to 80% of its initial value is commonly definedas the useful cycle life of a lithium-ion battery. Thus, the cycle lifeof the cell containing the non-encapsulated anode active material isapproximately 150 cycles. In contrast, the cycle life of the presentlyinvented cells (not just button cells, but large-scale full cells) istypically from 1,500 to 4,000.

EXAMPLE 2 High-Elasticity Polymer-Encapsulated Tin Oxide Particulates

Tin oxide (SnO₂) nano particles were obtained by the controlledhydrolysis of SnCl₄·5H₂O with NaOH using the following procedure:SnCl₄·5H₂O (0.95 g, 2.7 m-mol) and NaOH (0.212 g, 5.3 m-mol) weredissolved in 50 mL of distilled water each. The NaOH solution was addeddrop-wise under vigorous stirring to the tin chloride solution at a rateof 1 mL/min. This solution was homogenized by sonication for 5 m in.Subsequently, the resulting hydrosol was reacted with H₂SO₄. To thismixed solution, few drops of 0.1 M of H₂SO₄ were added to flocculate theproduct. The precipitated solid was collected by centrifugation, washedwith water and ethanol, and dried in vacuum. The dried product washeat-treated at 400° C. for 2 h under Ar atmosphere.

The high-elasticity polymer for encapsulation of SnO₂ nano particles wasbased on cationic polymerization and cross-linking of the cyanoethylpolyvinyl alcohol (PVA-CN) in succinonitrile (SN). The procedure beganwith dissolving PVA-CN in succinonitrile to form a mixture solution.This step was followed by adding an initiator into the solution. For thepurpose of incorporating some lithium species into the high elasticitypolymer, we chose to use LiPF₆ as an initiator. The ratio between LiPF₆and the PVA-CN/SN mixture solution was varied from 1/20 to 1/2 by weightto form a series of precursor solutions. Subsequently, particles of aselected anode active material (SnO₂ and graphene-embraced SnO₂particles) were introduced into these solutions to form a series ofslurries. The slurries were then separately subjected to amicro-encapsulation procedure to produce anode active material particleshaving entire exterior surfaces being coated with an embracing layer ofthe reacting mass, PVA-CN/LiPF₆. These embraced particles were thenheated at a temperature from 75 to 100° C. for 2 to 8 hours to obtainhigh-elasticity polymer-encapsulated anode active material particles.

The reacting mass, PVA-CN/LiPF₆, was cast onto a glass surface to formseveral films which were polymerized and cured to obtain cross-linkedpolymers having different degrees of cross-linking. Tensile testing wasalso conducted on these films and some testing results are summarized inFIG. 6(a). This series of cross-linked polymers can be elasticallystretched up to approximately 80% (higher degree of cross-linking) to400% (lower degree of cross-linking).

The battery cells from the high-elasticity polymer-encapsulatedparticulates (nano-scaled SnO₂ particles) and non-coated SnO₂ particleswere prepared using a procedure described in Example 1. FIG. 6(B) showsthat the anode prepared according to the presently inventedhigh-elasticity polymer-encapsulated particulate approach offers asignificantly more stable and higher reversible capacity compared toboth the un-coated SnO₂ particle-based anode and the graphene-wrappedSnO₂ particle-based anode. FIG. 6(C) indicates that the approach ofencapsulating the graphene-wrapped particles imparts a high level ofcycle stability to the anode by preventing direct contact of liquidelectrolyte with the anode active material and, thus, avoiding repeatedSEI breakage and formation (the primary source of battery capacitydecay).

EXAMPLE 3 Tin (Sn) Nano Particles Encapsulated by a PETEA-BasedHigh-Elasticity Polymer

For encapsulation of Sn nano particles, pentaerythritol tetraacrylate(PETEA), Formula 3, was used as a monomer:

The precursor solution was composed of 1.5 wt. % PETEA (C₁₇H₂₀O₈)monomer and 0.1 wt. % azodiisobutyronitrile (AIBN,C₈H₁₂N₄) initiatordissolved in a solvent mixture of 1,2-dioxolane(DOL)/dimethoxymethane(DME)(1:1 by volume). Nano particles (76 nm indiameter) of Sn were added into the precursor solution and wereencapsulated with a thin layer of PETEA/AIBN/solvent precursor solutionvia the spray-drying method (some solvent evaporated, but someremained). The precursor solution was polymerized and cured at 70° C.for half an hour to obtain particulates composed of high-elasticitypolymer-encapsulated particles.

The reacting mass, PETEA/AIBN (without Sn particles), was cast onto aglass surface to form several films which were polymerized and cured toobtain cross-linked polymers having different degrees of cross-linking.Tensile testing was also conducted on these films and some testingresults are summarized in FIG. 7(A). This series of cross-linkedpolymers can be elastically stretched up to approximately 25% (higherdegree of cross-linking) to 80% (lower degree of cross-linking)

For comparison, some amount of Sn nano particles was encapsulated by acarbon shell. Carbon encapsulation is well-known in the art.Un-protected Sn nano particles from the same batch were alsoinvestigated to determine and compare the cycling behaviors of thelithium-ion batteries containing these different types of particulatesor bare particles as the anode active material.

Shown in FIG. 7(B) are the discharge capacity curves of four coin cellshaving four different types of Sn particulates (protected) or particles(un-protected) as the anode active material: high-elasticitypolymer-encapsulated Sn particles, SBR rubber-encapsulated Sn particles,carbon-encapsulated Sn particles, and un-protected Sn particles. Theseresults have clearly demonstrated that elastomer encapsulation strategyprovides good protection against capacity decay of a lithium-ion batteryfeaturing a high-capacity anode active material. Carbon encapsulation isnot effective in providing the necessary protection. However, overallthe high-elasticity polymer protection strategy provides the mosteffective protection, enabling not only the highest reversible capacitybut also the most stable cycling behavior.

EXAMPLE 4 Si Nanowire-Based Particulates Protected by a High-ElasticityPolymer

Si nano particles and Si nanowires Si nano particles are available fromAngstron Energy Co. (Dayton, Ohio). Si nanowires, mixtures of Si andcarbon, and their graphene sheets-embraced versions were then furtherembraced with the semi-interpenetrating network polymer of ETPTA/EGMEAand the cross-linked BPO/ETPTA polymer (as in Example 1).

For the encapsulation of the various anode particles by the ETPTAsemi-IPN polymer, the ETPTA (Mw =428 g/mol, trivalent acrylate monomer),EGMEA (Mw=482 g/mol, monovalent acrylate oligomer), and2-hydroxy-2-methyl-l-phenyl-1-propanone (HMPP, a photoinitiator) weredissolved in a solvent (propylene carbonate, PC) to form a solution. Theweight ratio between HMPP and the ETPTA/EGMEA mixture was varied from0.2% to 2%. The ETPTA/EGMEA proportion in the solution was varied from1% to 5% to generate different encapsulation layer thicknesses. TheETPTA/EGMEA ratio in the acrylate mixture was varied from 10/0 to 1/9.

The air-suspension coating method was used to encapsulate anode activematerial particles into core-shell structures. The powder of core-shellparticulates having a reacting mass of ETPTA/EGMEA/HMPP was then exposedto UV irradiation for 20 s. The UV polymerization/cross-linking wasconducted using a Hg UV lamp (100 W), having a radiation peak intensityof approximately 2000 mW/cm² on the surfaces of the powder samples.

The above procedure produced Si nanowire particulates composed of Sinanowires encapsulated with a cross-linked ETPTA/EGMEA polymer shell.Some Si nanowires were coated with a layer of amorphous carbon and thenencapsulated with cross-linked ETPTA/EGMEA polymer. For comparisonpurposes, Si nanowires unprotected and those protected by carbon coating(but no polymer encapsulation), respectively, were also prepared andimplemented in a separate lithium-ion cell. In all four cells,approximately 25-30% of graphite particles were mixed with the protectedor unprotected Si nanowires (SiNW), along with 5% binder resin, to makean anode electrode. The cycling behaviors of these 4 cells are shown inFIG. 8, which indicates that high-elasticity polymer encapsulation of Sinanowires, with or without carbon coating, provides the most stablecycling response. Carbon coating alone does not help to improve cyclingstability by much.

EXAMPLE 5 Effect of Lithium Ion-Conducting Additive in a High-ElasticityPolymer Shell

A wide variety of lithium ion-conducting additives were added to severaldifferent polymer matrix materials to prepare encapsulation shellmaterials for protecting core particles of an anode active material. Wehave discovered that these polymer composite materials are suitableencapsulation shell materials provided that their lithium ionconductivity at room temperature is no less than 10⁻⁶ S/cm. With thesematerials, lithium ions appear to be capable of readily diffusing in andout of the encapsulation shell having a thickness no greater than 1 μm.For thicker shells (e.g. 10 μm), a lithium ion conductivity at roomtemperature no less than 10⁴ S/cm would be required.

TABLE 2 Lithium ion conductivity of various high-elasticity polymercomposite compositions as a shell material for protecting anode activematerial particles. Sample Lithium-conducting No. additive Elastomer(1-2 μm thick) Li-ion conductivity (S/cm) E-1p Li₂CO₃ + (CH₂OCO₂Li)₂70-99% PVA-CN 2.9 × 10⁻⁴ to 3.6 × 10⁻³ S/cm E-2p Li₂CO₃ + (CH₂OCO₂Li)₂65-99% ETPTA 6.4 × 10⁻⁴ to 2.3 × 10⁻³ S/cm E-3p Li₂CO₃ + (CH₂OCO₂Li)₂65-99% ETPTA/EGMEA 8.4 × 10⁻⁴ to 1.8 × 10⁻³ S/cm D-4p Li₂CO₃ +(CH₂OCO₂Li)₂ 70-99% PETEA 7.8 × 10⁻³ to 2.3 × 10⁻² S/cm D-5p Li₂CO₃ +(CH₂OCO₂Li)₂ 75-99% PVA-CN 8.9 × 10⁻⁴ to 5.5 × 10⁻³ S/cm B1p LiF +LiOH + Li₂C₂O₄ 60-90% PVA-CN 8.7 × 10⁻⁵ to 2.3 × 10⁻³ S/cm B2p LiF +HCOLi 80-99% PVA-CN 2.8 × 10⁻⁴ to 1.6 × 10⁻³ S/cm B3p LiOH 70-99% PETEA4.8 × 10⁻³ to 1.2 × 10⁻² S/cm B4p Li₂CO₃ 70-99% PETEA 4.4 × 10⁻³ to 9.9× 10⁻³ S/cm B5p Li₂C₂O₄ 70-99% PETEA 1.3 × 10⁻³ to 1.2 × 10⁻² S/cm B6pLi₂CO₃ + LiOH 70-99% PETEA 1.4 × 10⁻³ to 1.6 × 10⁻² S/cm C1p LiClO₄70-99% PVA-CN 4.5 × 10⁻⁴ to 2.4 × 10⁻³ S/cm C2p LiPF₆ 70-99% PVA-CN 3.4× 10⁻⁴ to 7.2 × 10⁻³ S/cm C3p LiBF₄ 70-99% PVA-CN 1.1 × 10⁻⁴ to 1.8 ×10⁻³ S/cm C4p LiBOB + LiNO₃ 70-99% PVA-CN 2.2 × 10⁻⁴ to 4.3 × 10⁻³ S/cmS1p Sulfonated polyaniline 85-99% ETPTA 9.8 × 10⁻⁵ to 9.2 × 10⁻⁴ S/cmS2p Sulfonated SBR 85-99% ETPTA 1.2 × 10⁻⁴ to 1.0 × 10⁻³ S/cm S3pSulfonated PVDF 80-99% ETPTA/EGMEA 3.5 × 10⁻⁴ to 2.1 × 10⁻⁴ S/cm S4pPolyethylene oxide 80-99% ETPTA/EGMEA 4.9 × 10⁻⁴ to 3.7 × 103⁴ S/cm

EXAMPLE 6 Cycle Stability of Various Rechargeable Lithium Battery Cells

In lithium-ion battery industry, it is a common practice to define thecycle life of a battery as the number of charge-discharge cycles thatthe battery suffers 20% decay in capacity based on the initial capacitymeasured after the required electrochemical formation. Summarized inTable 3 below are the cycle life data of a broad array of batteriesfeaturing presently invented elastomer-encapsulated anode activematerial particles vs. other types of anode active materials.

TABLE 3 Cycle life data of various lithium secondary (rechargeable)batteries. Initial Sample Type & % of anode active capacity Cycle life(No. ID Protective means material (mAh/g) of cycles) Si-1p PVA-CN 25% bywt. Si nano 1,120 1,666-2,050 encapsulation particles (80 nm) + 67%graphite + 8% binder Si-2p Carbon encapsulation 25% by wt. Si nano 1,242251 particles (80 nm) SiNW-1p PVA-CN 35% Si nanowires 1,258 2,555encapsulation (diameter = 90 nm) SiNW-2p PVA-CN + ethylene 45% Si nanoparticles, 1,760 2,250 (pre- oxide (50%) pre-lithiated or non-lithiated); 1,886 prelithiated (no pre-Li) no prelithiation) VO₂-1pETPTA 90%-95%, VO₂ nano 255 3,250 encapsulation ribbon Co₃O₄-2p ETPTA85% Co₃O₄ + 8% graphite 720 3,388 (Pre- encapsulation platelets + binderlithiated); 2,526 (no pre-Li) Co₃O₄-2p No encapsulation 85% Co₃O₄ + 8%graphite 725 266 platelets + binder SnO₂-2p ETPTA/EGMEA 75% SnO₂particles (3 μm 740 1,880 encapsulation initial size) SnO₂-2pETPTA/EGMEA 75% SnO₂ particles (87 nm 738 4,505 (Pre-Li); encapsulationin diameter) 2,767 (non pre- Li) Ge-1p PETEA encapsulated 85% Ge + 8%graphite 850 1,980 C-coated Ge platelets + binder Ge-2p Carbon-coated85% Ge + 8% graphite 856 120 platelets + binder Al—Li-1p PETEA Al/Lialloy (3/97) 2,850 2,660 encapsulation particles Al—Li-2p None Al/Lialloy particles 2,856 155 Zn—Li-1p PETEA C-coated Zn/Li alloy 2,6262,323 encapsulation (5/95) particles Zn—Li-2p None C-coated Zn/Li alloy2,631 146 (5/95) particles

These data further confirm the following features:

-   (1) The high-elasticity polymer encapsulation strategy is    surprisingly effective in alleviating the anode    expansion/shrinkage-induced capacity decay problems. Such a strategy    appears to have significantly reduced or eliminated the possibility    of repeated SEI formation that would other continue to consume    electrolyte and active lithium ions.-   (2) The encapsulation of high-capacity anode active material    particles by carbon or other protective materials without high    elasticity does not provide much benefit in terms of improving    cycling stability of a lithium-ion battery.-   (3) Pre-lithiation of the anode active material particles prior to    high-elasticity polymer encapsulation is beneficial to retaining    capacity.

(4) The high-elasticity polymer encapsulation strategy is alsosurprisingly effective in imparting stability to lithium metal or itsalloy when used as the anode active material of a lithium metal battery.

We claim:
 1. An anode active material layer for a lithium battery, saidanode active material layer comprising multiple particulates of an anodeactive material, wherein a particulate is composed of one or a pluralityof anode active material particles being embraced or encapsulated by athin layer of a high-elasticity polymer having a recoverable tensilestrain no less than 10% when measured without an additive orreinforcement, a lithium ion conductivity no less than 10⁻⁵ S/cm at roomtemperature, and a thickness from 0.5 nm to 10 μm.
 2. The anode activematerial layer of claim 1, wherein said high-elasticity polymer containsa cross-linked network of polymer chains having an ether linkage,nitrile-derived linkage, benzo peroxide-derived linkage, ethylene oxidelinkage, propylene oxide linkage, vinyl alcohol linkage, cyano-resinlinkage, triacrylate monomer-derived linkage, tetraacrylatemonomer-derived linkage, or a combination thereof in said cross-linkednetwork of polymer chains.
 3. The anode active material layer of claim1, wherein said high-elasticity polymer contains a cross-linked networkof polymer chains selected from nitrile-containing polyvinyl alcoholchains, cyanoresin chains, pentaerythritol tetraacrylate chains,pentaerythritol triacrylate chains, ethoxylated trimethylolpropanetriacrylate (ETPTA) chains, ethylene glycol methyl ether acrylate(EGMEA) chains, or a combination thereof.
 4. The anode active materiallayer of claim 1, wherein said anode active material is selected fromthe group consisting of: silicon (Si), germanium (Ge), tin (Sn), lead(Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium(Ti), nickel (Ni), cobalt (Co), and cadmium (Cd), alloys orintermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co,or Cd with other elements, oxides, carbides, nitrides, sulfides,phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al,Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, orlithium-containing composites, salts and hydroxides of Sn, lithiumtitanate, lithium manganate, lithium aluminate, lithium-containingtitanium oxide, lithium transition metal oxide, ZnCo₂O₄, prelithiatedversions thereof, particles of Li, Li alloy, or surface-stabilized Lihaving at least 60% by weight of lithium element therein, andcombinations thereof.
 5. The anode active material layer of claim 4,wherein said Li alloy contains from 0.1% to 10% by weight of a metalelement selected from Zn, Ag, Au, Mg, Ni, Ti, Fe, Co, V, or acombination thereof.
 6. The anode active material layer of claim 1,wherein said anode active material contains a prelithiated Si,prelithiated Ge, prelithiated Sn, prelithiated SnO_(x), prelithiatedSiO_(x), prelithiated iron oxide, prelithiated VO₂, prelithiated Co₃O₄,prelithiated Ni₃O₄, or a combination thereof, wherein x=1 to
 2. 7. Theanode active material layer of claim 1, wherein said anode activematerial is in a form of nano particle, nano wire, nano fiber, nanotube, nano sheet, nano belt, nano ribbon, nano disc, nano platelet, ornano horn having a thickness or diameter from 0.5 nm to 100 nm.
 8. Theanode active material layer of claim 7, wherein said anode activematerial has a dimension less than 20 nm.
 9. The anode active materiallayer of claim 1, wherein one or a plurality of said particles is coatedwith a layer of carbon or graphene disposed between said one or saidplurality of particles and said high-elasticity polymer layer.
 10. Theanode active material layer of claim 1, wherein said particulate furthercontains a graphite, graphene, or carbon material therein.
 11. The anodeactive material layer of claim 10, wherein said graphite or carbonmaterial is selected from polymeric carbon, amorphous carbon, chemicalvapor deposition carbon, coal tar pitch, petroleum pitch, meso-phasepitch, carbon black, coke, acetylene black, activated carbon, fineexpanded graphite particle with a dimension smaller than 100 nm,artificial graphite particle, natural graphite particle, or acombination thereof.
 12. The anode active material layer of claim 7,wherein said nano particle, nano wire, nano fiber, nano tube, nanosheet, nano belt, nano ribbon, nano disc, nano platelet, or nano horn iscoated with or embraced by a conductive protective coating selected froma carbon material, graphene, electronically conductive polymer,conductive metal oxide, or conductive metal coating.
 13. The anodeactive material layer of claim 12, wherein said nano particle, nanowire, nano fiber, nano tube, nano sheet, nano belt, nano ribbon, nanodisc, nano platelet, or nano horn is pre-intercalated or pre-doped withlithium ions to form a prelithiated anode active material having anamount of lithium from 0.1% to 54.7%% by weight of said prelithiatedanode active material.
 14. The anode active material layer of claim 1,wherein said high-elasticity polymer has a lithium ion conductivity noless than 10⁻⁴ S/cm.
 15. The anode active material layer of claim 1,wherein said high-elasticity polymer has a lithium ion conductivity noless than 10⁻³ S/cm
 16. The anode active material layer of claim 1,wherein said high-elasticity polymer is a neat polymer having noadditive or filler dispersed therein.
 17. The anode active materiallayer of claim 1, wherein said high-elasticity polymer contains from0.1% to 50% by weight of a lithium ion-conducting additive dispersedtherein, or contains therein from 0.1% by weight to 10% by weight of areinforcement nano filament selected from carbon nanotube, carbonnano-fiber, graphene, or a combination thereof.
 18. The anode activematerial layer of claim 1, wherein said high-elasticity polymer forms amixture with an elastomer selected from natural polyisoprene, syntheticpolyisoprene, polybutadiene, chloroprene rubber, polychloroprene, butylrubber, styrene-butadiene rubber, nitrile rubber, ethylene propylenerubber, ethylene propylene diene rubber, epichlorohydrin rubber,polyacrylic rubber, silicone rubber, fluorosilicone rubber,perfluoroelastomers, polyether block amides, chlorosulfonatedpolyethylene, ethylene-vinyl acetate, thermoplastic elastomer, proteinresilin, protein elastin, ethylene oxide-epichlorohydrin copolymer,polyurethane, urethane-urea copolymer, or a combination thereof.
 19. Theanode active material layer of claim 1, wherein said high-elasticitypolymer is mixed with a lithium ion-conducting additive to form acomposite wherein said lithium ion-conducting additive is dispersed insaid high-elasticity polymer and is selected from Li₂CO₃, Li₂O, Li₂C₂O₄,LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S,Li_(x)SO_(y), or a combination thereof, wherein X═F, Cl, I, or Br, R=ahydrocarbon group, x=0-1, y=1-4.
 20. The anode active material layer ofclaim 1, wherein said high-elasticity polymer is mixed with a lithiumion-conducting additive to form a composite wherein said lithiumion-conducting additive is dispersed in said high-elasticity polymer andis selected from lithium perchlorate, LiClO₄, lithiumhexafluorophosphate, LiPF₆, lithium borofluoride, LiBF₄, lithiumhexafluoroarsenide, LiAsF₆, lithium trifluoro-metasulfonate, LiCF₃SO₃,bis-trifluoromethyl sulfonylimide lithium, LiN(CF₃SO₂)₂, lithiumbis(oxalato)borate, LiBOB, lithium oxalyldifluoroborate, LiBF₂C₂O₄,lithium oxalyldifluoroborate, LiBF₂C₂O₄, lithium nitrate, LiNO₃,Li-Fluoroalkyl-Phosphates, LiPF₃(CF₂CF₃)₃, lithiumbisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTF SI, an ionic liquid-basedlithium salt, or a combination thereof.
 21. The anode active materiallayer of claim 1, wherein said high-elasticity polymer is mixed with anelectron-conducting polymer selected from polyaniline, polypyrrole,polythiophene, polyfuran, a bi-cyclic polymer, a sulfonated derivativethereof, or a combination thereof.
 22. The anode active material layerof claim 1, wherein the high-elasticity polymer forms a mixture or blendwith a lithium ion-conducting polymer selected from poly(ethylene oxide)(PEO), Polypropylene oxide (PPO), poly(acrylonitrile) (PAN), poly(methylmethacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a sulfonatedderivative thereof, or a combination thereof.
 23. A powder mass of ananode active material for a lithium battery, said powder mass comprisingmultiple particulates wherein at least a particulate is composed of oneor a plurality of anode active material particles being embraced orencapsulated by a thin layer of a high-elasticity polymer having arecoverable tensile strain from 10% to 700% when measured without anadditive or reinforcement, a lithium ion conductivity no less than 10⁻⁵S/cm at room temperature, and a thickness from 0.5 nm to 10 μm.
 24. Thepowder mass of claim 23, further comprising graphite particles, carbonparticles, meso-phase microbeads, carbon or graphite fibers, carbonnanotubes, graphene sheets, or a combination thereof.
 25. The powdermass of claim 23, wherein said anode active material is lithiated tocontain from 0.1% to 54.7% by weight of lithium.
 26. The powder mass ofclaim 23, wherein one or a plurality of said particles is coated with alayer of carbon or graphene disposed between said one or a plurality ofparticles and said high-elasticity polymer layer.
 27. A lithium batterycontaining an optional anode current collector, the anode activematerial layer as defined in claim 1, a cathode active material layer,an optional cathode current collector, an electrolyte in ionic contactwith said anode active material layer and said cathode active materiallayer, and an optional porous separator.
 28. The lithium battery ofclaim 27, which is a lithium-ion battery, lithium metal battery,lithium-sulfur battery, lithium-selenium battery, or lithium-airbattery.
 29. A method of manufacturing a lithium battery, said methodcomprising: (a) providing a cathode and an optional cathode currentcollector to support said cathode; (b) providing an anode and anoptional anode current collector to support said anode; (c) providing anelectrolyte in contact with the anode and the cathode and an optionalseparator electrically separating the anode and the cathode; wherein theoperation of providing the anode includes providing multipleparticulates of an anode active material, wherein a particulate iscomposed of one or a plurality of anode active material particles beingembraced or encapsulated by a thin layer of a high-elasticity polymerhaving a recoverable tensile strain from 10% to 700% when measuredwithout an additive or reinforcement, a lithium ion conductivity no lessthan 10⁻⁵ S/cm at room temperature, and a thickness from 0.5 nm to 10μm.
 30. The method of claim 29, wherein said high-elasticity polymer hasa thickness from 1 nm to 100 nm.
 31. The method of claim 29, whereinsaid high-elasticity polymer has a lithium ion conductivity from 1×10⁻⁵S/cm to 2×10⁻² S/cm.
 32. The method of claim 29, wherein saidhigh-elasticity polymer has a recoverable tensile strain from 30% to300%.
 33. The method of claim 29, wherein said high-elasticity polymercontains a cross-linked network polymer chains having an ether linkage,nitrile-derived linkage, benzo peroxide-derived linkage, ethylene oxidelinkage, propylene oxide linkage, vinyl alcohol linkage, cyano-resinlinkage, triacrylate monomer-derived linkage, tetraacrylatemonomer-derived linkage, or a combination thereof in said cross-linkednetwork of polymer chains.
 34. The method of claim 29, wherein saidhigh-elasticity polymer contains a cross-linked network of polymerchains selected from nitrile-containing polyvinyl alcohol chains,cyanoresin chains, pentaerythritol tetraacrylate chains, pentaerythritoltriacrylate chains, ethoxylated trimethylolpropane triacrylate (ETPTA)chains, ethylene glycol methyl ether acrylate (EGMEA) chains, or acombination thereof.
 35. The method of claim 29, wherein said providingmultiple particulates includes encapsulating or embracing said one or aplurality of anode active material particles with said thin layer ofhigh-elasticity polymer using a procedure selected from pan coating, airsuspension, centrifugal extrusion, vibrational nozzle, spray-drying,ultrasonic spraying, coacervation-phase separation, interfacialpolycondensation, in-situ polymerization, matrix polymerization, or acombination thereof.
 36. The method of claim 29, wherein said providingmultiple particulates includes encapsulating or embracing said one or aplurality of anode active material particles with a mixture of saidhigh-elasticity polymer with an elastomer, an electronically conductivepolymer, a lithium-ion conducting material, a reinforcement material, ora combination thereof.
 37. The method of claim 36, wherein said lithiumion-conducting material is dispersed in said high-elasticity polymer andis selected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof,wherein X═F, Cl, I, or Br, R=a hydrocarbon group, x=0-1, y=1-4.
 38. Themethod of claim 36, wherein said lithium ion-conducting material isdispersed in said high-elasticity polymer and is selected from lithiumperchlorate, LiClO₄, lithium hexafluorophosphate, LiPF₆, lithiumborofluoride, LiBF₄, lithium hexafluoroarsenide, LiAsF₆, lithiumtrifluoro-metasulfonate, LiCF₃SO₃, bis-trifluoromethyl sulfonylimidelithium, LiN(CF₃SO₂)₂, lithium bis(oxalato)borate, LiBOB, lithiumoxalyldifluoroborate, LiBF₂C₂O₄, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-Fluoroalkyl-Phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof.
 39. The method of claim 29,wherein said anode active material is selected from the group consistingof: silicon (Si), germanium (Ge), tin (Sn), zinc (Zn), aluminum (Al),titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); oxides,carbides, nitrides, sulfides, phosphides, selenides, and tellurides ofSi, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and theirmixtures, composites, or lithium-containing composites; lithiumtitanate, lithium manganate, lithium aluminate, lithium-containingtitanium oxide, lithium transition metal oxide, ZnCo₂O₄; prelithiatedversions thereof; mixtures thereof with a carbon, graphene, or graphitematerial; particles of Li, Li alloy, or surface-stabilized Li having atleast 60% by weight of lithium element therein; and combinationsthereof.
 40. The method of claim 29, wherein said one or a plurality ofanode active material particles is coated with a layer of carbon orgraphene disposed between said one or said plurality of particles andsaid high-elasticity polymer layer.
 41. The method of claim 29, whereinsaid one or a plurality of anode active material particles is mixed witha carbon, graphene, or graphite material to form a mixture and saidmixture is embraced by one or a plurality of graphene sheets disposedbetween said mixture and said high-elasticity polymer layer.
 42. Themethod of claim 29, wherein said one or plurality of anode activematerial particles are mixed with a carbon material, a graphitematerial, and/or graphene sheets to form a mixture that is embraced byexternal graphene sheets to form graphene-embraced anode active materialparticulates, which are then embraced or encapsulated by thehigh-elasticity polymer.